Problem: Michael ate 5 slices of pizza. Christopher ate 1 slice. If Michael ate $\dfrac{5}{7}$ of the pizza, what fraction of the pizza is remaining?
If 5 slices represent $\dfrac{5}{7}$ of the pizza, there must have been a total of 7 slices. $\text{fraction of pizza remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 6 slices, which leaves 1 out of 7 slices remaining. There is $\dfrac{1}{7}$ of the pizza remaining.